The present invention relates to substance combinations as vapor phase corrosion inhibitors (corrosion inhibitors with evaporation or sublimation capacity, vapor phase corrosion inhibitors VpCI, volatile corrosion inhibitors, VCI) and methods for their application for the protection of common commodity metals such as iron, chrome, nickel, aluminum, copper and their alloys as well as galvanized steels against corrosion in moist air climates.
Compounds which had been identified as corrosion inhibitors and which also tend towards evaporation or sublimation under normal conditions and therefore can reach the metal surfaces to be protected via the gaseous phase have been used for several decades for the temporary corrosion protection of metal objects within enclosed spaces, for example in packaging, control cabinets or display cabinets. The protection of metal components against corrosion during storage and transport in this way is the clean alternative to temporary corrosion protection with oils, fats or waxes.
All temporary metal corrosion protection measures against the effect of air-saturated aqueous media or condensed water films are known to be aimed at conserving the primary oxide layer (primary oxide layer, POL) always present on commodity metals following their first contact with the atmosphere against chemical and mechanical degradation (compare for example: E. Kunze (publisher), Corrosion and Corrosion Protection, Volume 3, Wiley-VCH, Berlin, N.Y. 2001, p. 1679-1756). In order to achieve this by the application of corrosion inhibitors preferably acting via the gaseous phase, it should however be taken into account that common commodity metals and the POL always present on their surfaces have different chemical characteristics. Vapor phase corrosion inhibitors must therefore be selected depending on the type of metal to be protected in principle (compare for example: U.S. Pat. Nos. 4,374,174, 6,464,899, 6,752,934 B2, 7,824,482 B2 and 8,906,267 B2).
For objects and constructions made from different metals and possibly also existing in different processing conditions (rough, smoothed, polished etc.), combinations of different corrosion inhibitors are consequently also required in order to guarantee respective reliable temporary corrosion protection for the metals and surface conditions in question within one and the same container or a common packaging. As such mixed metal objects and components are technically the most prevalent today from our experience, the determination of suitable substance combinations of corrosion inhibitors acting via the gaseous phase is of ever increasing importance.
The use of such combinations of volatile corrosion inhibitors (VpCI/VCI) in practice should be possible in particular in view of already established applications, although adapted to the various sensibilities of the metals and surface conditions to be protected in air with various humidity and compositions as well as with regard to the compatibility of individual components amongst each other.
In order to realize reliable corrosion protection for metal components inside containers and packaging, the walls of which are permeable for water vapor-containing air (paper, plastic film and others) by means of VpCI/VCI it must be guaranteed that the active substances are as a rule released sufficiently quickly from the respective depository through evaporation and/or sublimation, through diffusion and convection within the closed packaging reach the metal surfaces to be protected and form an adsorption film there before water can condense from moist air in the same place.
The time known as a so-called development phase (conditioning or incubation time), during which the conditions for VCI corrosion protection are established after closing the container/the packaging, can naturally not be too long for above averagely corrosion susceptible metal surfaces, as the corrosion process will otherwise have started before the VCI molecules reach the vicinity of the metal surface.
Depending on the type of metal to be protected and the existing surface conditions one must therefore not only use a suitable combination of VpCI/VCI components, but must also apply these in such a way that the so-called development phase required for developing their effect is adapted to fulfil the respective requirements.
Solids that tend towards sublimation even under normal conditions are known to adjust their evaporation equilibrium with the gaseous phase increasingly easily as their specific surface increases. The provision of such corrosion inhibitors in powder form with the smallest possible particle size can thus be considered a basic requirement for the setting of the shortest possible development phase. VpCI/VCI in the form of finely dispersed powders, packed in pouches made of a material that is permeable for the vaporous active substances (for example paper bags, porous polymer film, perforated capsules) have therefore long been in commercial use. To expose them within closed packaging in addition to the metal components to be protected is the simplest form of a practical application of VpCI/VCI (compare for example: E. Vuorinen, E. Kalman, W. Focke, Introduction to vapor phase corrosion inhibitors in metal packaging, Surface Engng. 29(2004) 281 pp., U.S. Pat. Nos. 4,973,448, 5,393,457, 6,752,934 B2, 8,906,267 B2, 9,435,037 and EP 1 219 727 A2). The development phases that can be realized with the same can also be regulated with the permeability of the walls of such depots. If mixtures of different substances are to be used instead of individual corrosion inhibitors it must additionally be guaranteed that they neither chemically react with each other nor lead to a formation of agglomerates, as this would prevent their emission from the depot as well as their required chemisorptions on the metal surfaces to be protected, or would at least strongly affect the same.
In modern packaging materials for temporary corrosion protection the VpCI/VCIs are normally already integrated these days, so that their technical application is simple and can also be automated. Paper, cardboard, foam or textile fleece materials with a VCI containing coatings are common here as well as polymer substrate materials into which the active VCI substances in question are integrated so that their emission from the same remains possible. Different variants are for example suggested in U.S. Pat. Nos. 3,836,077, 3,967,926, 4,124,549, 4,290,912, 5,209,869, 5,332,525, 5,393,457, 6,752,934 B2, 7,824,482, 8,906,267 B2, JP 4.124.549, EP 0.639.657 and EP 1.219.727, always with the aim of inserting the VpCI/VCIs into a depot, such as for example into capsules, coatings or gas permeable plastic films respectively in such a way that a product from which the VCI components can continuously evaporate or sublimate results. To achieve this with combinations of several substances and also to initiate a physically approximately equivalent behavior with regard to migration inside the depot and emission from the same for every component, is however complicated by nature and clearly explains why optimal VCI corrosion protection characteristics are realized only rarely for many applications with the substance combinations known to date, namely for mixed metal objects and components. Different particle sizes of the components of a substance combination can already cause defects in an individual case if the structure-dependent pores of the walls of the active substance depot are for example not big enough to guarantee identical conditions with regard to permeation and sublimation of individual molecules or molecule associates of the active substance mixture.
From experience the integration of VpCI/VCIs into a coating agent allows a relatively easy manufacture of coatings for flat packaging materials (paper, cardboard, foam, textile fleece material etc.) these days, from which the respective VpCI/VCIs can be released at emission rates that guarantee comparatively short development phases for VCI corrosion protection. This requires the selection of a suitable coating agent that finely disperses the substance combination integrated in powder form in the first instance and absorbs the same to a sufficiently high filling degree, and cross-links on the respective substrate into a well adhering, porous layer from which the respective VpCI/VCIs can then once again sublimate without much resistance. The application quantity of VpCI/VCI coating agent also offers the possibility of adapting the VpCI/VCI depot to the conditions of the shortest possible development phases.
Manufacturing VpCI/VCI containing packaging material in that the active substances are dispersed in a suitable coating agent and applied to a flat substrate material has therefore been practiced for a long time. Methods of this type with various active substances and coating agents are for example described in JP 61.227.188, JP 62.063.686, JP 63.028.888, JP 63.183.182, JP 63.210.285, U.S. Pat. Nos. 5,958,115, 8,906,267 B2 and 9,518,328 B1.
The integration of VpCI/VCIs in polymer substrate materials, preferably in polyolefins (PO) such as polyethylene (PE) and polypropylene (PP), and the provision of VpCI/VCI-emitting films and further PO products (granulates, trays, etc.), for example as suggested in U.S. Pat. Nos. 4,124,549, 4,290,912, 5,139,700, 6,464,899 B1, 6,752,934 B2, 6,787,065 B1, 7,824,482, EP 1 218 567 A1 and EP 1 641 960 B1, is known to be practiced to a particularly high extent these days, for the reason alone that these products can be advantageously applied for an automation of packaging processes.
These polymer-based VpCI/VCI products do however normally have the disadvantage that the VpCI/VCIs incorporated during extrusion via the polymer melt are present in a powder form or relatively firmly enclosed in coatings in the polymer matrix, unlike the VpCI/VCI deposits described above, and their emission from the same is thus possible only with comparative difficulty. In the VpCI/VCI films normally used with layer thicknesses d within a range of 60 μm≤150 μm today it is also not possible to use the high specific active substance concentrations that can for example be accommodated in VpCI/VCI coatings. In addition losses of VpCI/VCI components that are difficult to control normally occur during the extrusion of the respective master batches and films due to the thermal load that occurs. Experience shows that none of the currently known VpCI/VCI substrate combinations can provide films suitable for the VCI corrosion protection of above averagely corrosion sensitive metal surfaces, for the simple reason that it has not been possible for the said reasons to set the necessary, relatively short development phases. VpCI/VCI films commercially available today have therefore primarily been used as technologically easy-to-apply mass articles to date without being able to satisfy higher requirements regarding their VCI corrosion protection characteristics.
A number of suggestions have become known for improving this situation and to profile packaging with polymer films to be more effective with regard to incorporated VpCI/VCI systems. All measures that enable the emission of VpCI/VCI components integrated into polymer films in just one direction appear expedient here, oriented on the metal component to be protected in the packaging, and for equipping the opposite side as a barrier.
It is for example suggested in U.S. Pat. Nos. 5,393,457 A1, 7,763,213 B2 and 8,881,904 B2 to encase the packaging primarily manufactured with film containing VpCI/VCI wrapped around the metal component to be protected with an additional barrier film. U.S. Pat. No. 5,137,700 however envisages that the outside of the VpCI/VCI film is laminated with a metal or plastic layer acting as a barrier prior to use as a packaging material and to stipulate the film equipped with the VpCI/VCI component as the inside when packing the metal component to be protected. The suggestion according to U.S. Pat. No. 8,881,904 B2 of manufacturing the VpCI/VCI film in a multi-layered way through co-extrusion from the start and to not dose the layer positioned as the outside with a VpCI/VCI master batch will from our experience not lead to this outer layer of the film then functioning as a barrier against the permeation of the vaporous VpCI/VCI components. Instead the emission of VpCI/VCI components from the internal layer into the gas space of the packaging will normally be worse, because the degradation of the concentration gradient required for this already commences through migration of the active substances into the initially active substance-free outer layer during storage of the co-extrusion film on a roll and will result in a lessening of the VCI effect.
As one has been unable to date to achieve an acceleration of the emission of the VpCI/VCI components in question into the interior of the closed packaging by using an additional barrier film or by equipping the outside of a VpCI/VCI containing film as a diffusion barrier, further measures have been suggested for shortening the so-called development phase of the respective integrated VpCI/VCI system in film packaging in such a way that improved VCI corrosion protection characteristics result. One step in this direction is for example the coating of the inside of a polymer film with a gel containing the VpCI/VCI components, fixed under a gas permeable inner film made of Tyvek® 1059 (DuPont) (compare U.S. Pat. No. 7,763,213 B2), which supposedly also makes it possible to stipulate much higher quantity proportions of the VpCI/VCI components than is possible with direct integration into a polymer film by means of extrusion.
A further, somewhat equivalent way consists of the introduction of individual or several VpCI/VCI components into a suitable adhesive in order to then coat the inside of polymer films with the same as required (compare for example: EP 2 347 897 A1, EP 2 730 696 A1, EP 2 752 290 A1 and US 2015/0018461 A1). If an adhesive that is compatible with the introduced VpCI/VCI components has been selected and cures as a porous layer, one will indeed realize higher emission rates for these components than for those that would result from films into which the VpCI/VCI components were integrated during extrusion.
And finally the suggestions of interspersing a VpCI/VCI system directly in the film serving as packaging material as a finely dispersed powder (compare for example: U.S. Pat. No. 8,603,603), to place it near the metal components to be protected in the form of high-filled briquettes (so-called premix, compare U.S. Pat. No. 6,787,065 B1), or of introducing it in the form of fine granulates to a flat porous foam, to the other side of which a thin polymer film has been laminated (compare for example: U.S. Pat. Nos. 5,393,457 and 9,435,037 B2) represent further possibilities of providing a low-resistance subliming VpCI/VCI system with a relatively high quantity proportion inside film packaging.
All of these suggestions have however been too material- and cost-intensive to date, so that in practice one preferably reverts from experience to the application variants of the VpCI/VCI systems already mentioned and considered as classics when designing high-performance corrosion protection packaging.
As we know these also include VpCI/VCI-containing oils, wherein requirements for products suitable for the VCI corrosion protection of components consisting of different metals and in different processing conditions in particular are ever increasing. Such a VpCI/VCI-containing oil is known to have not only to protect the metal substrate in question, onto which it is applied as a thin film, but also surface areas of the same component or neighboring metal objects that cannot be coated with an oil film due to their geometry (for example bores, narrow grooves, folded sheet metal layers) against corrosion. As with the VpCI/VCI depot already mentioned it is once again necessary that the VpCI/VCI components now emitted from the oil, as the carrier material, reach the surface areas of metal components not covered with the oil inside closed spaces (for example packaging, containers, hollow spaces) via the vapor phase, and form a corrosion protective adsorption film there.
VpCI/VCI oils are for example described in patent documents U.S. Pat. Nos. 919,778, 3,398,095, 3,785,975, 8,906,267, 1,224,500 and JP 07145490 A. As these VpCI/VCI oils emit volatile corrosion inhibitors and also protect areas of metal surfaces not covered by an oil against corrosion via the gaseous phase, they clearly differ from conservation oils, the corrosion protection characteristics of which are improved through introduction of non-volatile corrosion inhibitors that are effective only upon direct contact. Such corrosion protection oils are for example described in patent documents U.S. Pat. Nos. 5,681,506, 7,014,694 B1 and WO 2016/022406 A1.
Most of the currently known VpCI/VCI oils have however been profiled only for the VCI corrosion protection of ferrous materials. They normally contain higher quantity proportions of one or more amines, so that a relatively high concentration gradient can become effective inside closed packaging for their migration within the oil phase and their emission from the same to atmosphere. The development phase required for developing its VCI effect is then also correspondingly short. The amine reaching the metal surface to be protected via the gaseous phase ensures an alkaline surface pH value in the water condensed from moist air there, at which the POL of conventional ferrous materials is consistent (see for example: Kunze (publisher) loc. cit.). From experience these amine-based VpCI/VCI oils are however not suitable for the VCI corrosion protection of non-ferrous metals (for example Al and Cu base materials) and galvanized steel, as their POL will degrade at these high surface pH values whilst forming hydroxo complexes, followed by corrosion.
It has been common practice for many years to use amines that already have a vapor or sublimation pressure under normal conditions as VCI/VpCIs, and this has been described in numerous patents (compare for example: E. Vuorinen, et al., loc.cit. and U.S. Pat. No. 8,906,267 B2). Today one preferably limits this to the cyclic amines dicyclohexylamine and cyclohexylamine (compare for example: U.S. Pat. Nos. 4,275,835, 5,393,457, 6,054,512, 6,464,899 B1, 9,435,037 and 9,518,328 B1) as well as the various primary and tertiary alkanolamines such as 2-aminoethanol and triethanolamine, or corresponding substitutes (compare for example: E. Vuorinen, et al., loc.cit. as well as U.S. Pat. Nos. 6,752,934 B2 and 8,906,267 B2).
Secondary amines such as diethanolamine, morpholine, piperidine and many others previously recommended for preferred use, are however rarely considered for technical use now that it has become known that these are easily nitrosated into carcinogenic N-nitrosamines even in air under normal conditions.
As the cyclic amines and amino alcohols are liquid under normal conditions, they must first be transferred into a solid condition by forming salts for the above-mentioned applications (for example for powder-containing emitters or the introduction into polymer carrier materials). The respective amine carbonates, nitrites, nitrates, molybdates and carboxylates, and of the latter primarily the amine benzoates and caprylates, are the most common VCI/VpCIs used for the corrosion protection of ferrous materials today (compare for example: EP 0 990 676 B1, U.S. Pat. Nos. 4,124,549, 5,137,700, 393,457, 6,464,899 A1, 8,603,603 B2, 9,435,037, 9,518,328 B2 and JP 2016-117920 A).
With the amine carboxylates the amine compounds as well as the associated carboxylic acid in particular are volatile and therefore both reach the metal surfaces to be protected via the vapor phase. The surface pH value generated there in the presence of water vapor will then normally lie within the neutral range, which mostly influences the corrosion protection effect for non-ferrous metals in a positive way. Amines alone however will lead to higher surface pH values within the alkaline range and will, as already mentioned, lead to corrosion phenomena primarily with aluminum base materials and galvanized steels.
As amines normally already have higher vapor pressures under normal conditions than the associated carboxylic acids we know from experience that the preferred enrichment of the amine components will take place over time, primarily with films into which amine carboxylates were introduced as VCI/VpCIs. This does however of necessity also result in films of this kind that have been used for some time or stored mainly emitting only the remaining carboxylic acid. However, if only carboxylic acids reach the metal surfaces to be protected via the vapor phase then low acidic surface pH values will occur there in the presence of moist air. This prevents an adsorption of the carboxylate species on the POL of the metal surface to be protected and therefore counteracts corrosion inhibition (compare for example: N. S. Nhlapo, thesis “TGA-FTIR study of vapors released by volatile corrosion inhibitor model systems”, Fac. Chem. Engng., Univ. of Pretoria, S.A., July 2013). A formation of visible corrosion products will however initially not occur with ferrous material in particular because its POL is known to be converted into a thin iron carboxylate cover layer that is not perceivable without modern optical methods. As such thin salt-like conversion layers are however porous, corrosion of the iron-based material present in the pores will in the end result with continued exposure in moist air accompanied by hydrogen generation with a formation of visible corrosion products, as is the case practically straight away with Al materials and galvanized steels under the influence of acidic aqueous media. From current experience VCI/VpCI preparations with amine carboxylates are therefore suitable at most for the relatively short-term corrosion protection of ferrous materials, and are not suitable for protecting mixed metal components.
The same applies for the application of nitrites acting as passivators. With these salts of nitrous acid it is possible to achieve a spontaneous reproduction of the POLs of ferrous materials if these have been destroyed through partial chemical dissolving or localized mechanical abrasion (abrasion, erosion) (compare for example: E. Vuorinen, et al., loc. cit. and U.S. Pat. No. 6,752,934 B2). They have therefore been used as VCI/VpCIs for some time. The relatively readily volatile salt dicyclohexyl ammonium nitrite (DICHAN) in particular has been used as a VCI for the protection of ferrous materials for more than 70 years (compare for example Vuorinen et al., loc. cit.). This DICHAN has been mentioned as a component of VCI/VpCI compositions in numerous patent documents up until recent times (for example: U.S. Pat. Nos. 5,393,457, 6,054,512, 6,752,934 B2, 9,435,037, JP 2016-117920 A and EP 0 990 676 B1), although only ever for the VCI corrosion protection of ferrous materials. All known recipes containing the DICHAN, in most cases supplemented with further components such as water-free molybdates, carboxylates, benzotriazole or tolyltriazole (compare for example: U.S. Pat. Nos. 5,137,700, 5,393,457 and 6,054,512) have so far proven themselves as unsuitable for the protection of mixed metal components with aluminum and copper materials as well as for galvanized steels for various reasons.
With the aim of creating VpCI/VCI packaging materials that can be used not only for the protection of ferrous materials, but at least also for galvanized steels and aluminum materials, various amine-free VpCI/VCIs systems where a nitrous acid salt (ammonium or alkali nitrite) with further sublimation-capable substances, such as for example various saturated or unsaturated carboxylic acids or their alkaline salts, a polysubstituted phenol and/or an aliphatic ester of a hydroxybenzoic acid are combined, have been suggested (compare for example: U.S. Pat. Nos. 4,290,912, 6,464,899 B1, 6,752,934, 6,787,065 B1, EP 1 641 960 B1 and KR 1020160011874 A).
Other suggestions prefer amine- and nitrite-free substance combinations instead, for example consisting of various saturated or unsaturated carboxylic acids or their alkaline salts in combination with an aliphatic ester of a mono- or dihydroxybenzoic acid, an aromatic amide and, if necessary, completed with benzotriazole or tolyltriazole for the protection of Cu materials (compare for example: U.S. Pat. Nos. 4,124,549, 4,374,174, 7,824,482).
It has been possible, by admixing selected sublimatable, water-insoluble but water vapor-volatile polysubstituted phenols (compare for example: U.S. Pat. Nos. 4,290,912, 6,752,934, 7,824,482, EP 1 641 960 B1), bicyclic terpenes and aliphatic-substituted naphthalenes (compare for example: U.S. Pat. No. 6,752,934), to improve the emission of the VpCI/VCI components contained in the respective substance combination already under normal conditions, in particular in air with a higher relative humidity, and to bring the same to the level common for amines. However, the resulting VCI corrosion protection for ferrous as well as for other common non-ferrous metals containing VpCI/VCI components still requires comparatively high-filled active substance depots, as always higher quantity proportions of the substances acting as carrier must also be accommodated in addition to the respective VpCI/VCI components.
Good corrosion protection could be realized for objects consisting of several metals and surface conditions with VpCI/VCI combinations consisting of an aminoalkyldiol with C3 to C5, a monoalkyl carbamide, a preferably polysubstituted pyrimidine and benzotriazole suggested in U.S. Pat. No. 8,906,267 B2, without admixing substances acting as carriers.
Inorganic and organic salts such as the alkali nitrites, nitrates and carboxylates are in any case unsuitable for the introduction of VpCI/VCI combinations into mineral or synthetic oils in particular, as they are not sufficiently soluble in the same. Such VpCI/VCI oils have therefore in the past been mainly formulated through use of amines as VCI components (compare for example: U.S. Pat. Nos. 919,778, 1,224,500, 3,398,095, 3,785,975 and JP 07145490 A), sometimes supplemented with further volatile additives such as C6 to C12 alkyl carboxylic acids and esters of unsaturated fatty acids (compare U.S. Pat. No. 3,398,095). JP 07145490 A however claims preparations with ethanolamine carboxylates, morpholine, cyclohexylamine and various sulphonates. All of these recipes do however have in common that only the amine components are emitted under normal conditions, i.e. at temperatures of <60° C., and become active as VpCI/VCIs.
Such VpCI/VCI oils are therefore suitable only for the VCI corrosion protection of ferrous materials. With zinc and aluminum they are known to normally cause an excessive alkalization of the surfaces together with condensed water, the consequence of which is strong corrosion whilst forming zincates or aluminates, before hydroxides and basic carbonates are finally created, which are commonly known as white rust. Copper materials however often suffer corrosion under the influence of amines whilst forming Cu amine complexes.
To counteract this defect the VpCI/VCI combination of an aminoalkyldiol with C3 to C5, a monoalkyl carbamide, a preferably polysubstituted pyrimidine and benzotriazole suggested in U.S. Pat. No. 8,906,267 B2 can be introduced into a mineral oil or a synthetic oil via a solubilizer in such a way that a VpCI/VCI oil is created, with which good VCI corrosion protection can be provided for a wide range of common commodity metals. It has now been found to be a disadvantage that only relatively small quantity proportions of the VpCI/VCI components can be introduced, so that the very good VCI effect of fresh preparations increasingly deteriorates with long-term applications. The same was found when such a VpCI/VCI oil was diluted with a conventional mineral oil.
New VpCI/VCI systems, the use of which is not connected with the described disadvantages in practice, are therefore required, in particular to satisfy the requirement for oils equipped with VpCI/VCI for managing the temporary corrosion protection of ferrous and non-ferrous metals with construction-related small hollow spaces. Preparations that can be processed to produce not only a VpCI/VCI oil, but at least also VpCI/VCI dispensers (mixtures of particulate VpCI/VCI components in pouches, capsules etc.) and coated VpCI/VCI packaging materials (for example paper, cardboard, foam) are of particular interest here.
Particularly effective VCI corrosion protection packaging characterized by a long service life can be produced by combining such VpCI/VCIs that are compatible with each other in an unlimited way for the said applications, for example as preservation packaging for engine blocks treated with the VpCI/VCI oil in containers closed with a lid, in which VCI-emitting pouches, capsules etc. or VCI-coated paper or foam cuttings are also placed, in order to ensure constant saturation of the gas space of the containers in question with the VpCI/VCI components even during long-time storage as a requirement for the maintenance of VCI corrosion protection.
It is the objective of the invention to provide improved evaporation- or sublimation-capable corrosion-inhibiting substances and substance combinations in view of the above listed disadvantages of conventional volatile corrosion inhibitors acting via the vapor phase, which can be supplied as a powder mixture as well as introduced into coatings and oils under the interesting climate conditions prevailing in practice in technical packaging and similarly in closed containers with sufficient speed from the corresponding depot, for example a pouch containing the VpCI/VCI components, a coating containing the VpCI/VCI components on a carrier such as paper, cardboard or foam, or through evaporating or sublimating from an oil containing the VpCI/VCI components, to ensure conditions on the surface of metal components located in this space following adsorption and/or condensation there under which common commodity metals are reliably protected against atmospheric corrosion.
According to the invention these objectives could be achieved with the provision of the substance combination according to the invention.